One in 26,000 births results in achondroplasia, a common cause of dwarfism caused by an autosomal dominant genetic disorder. Bone formation and longitudinal bone growth in long bones, ribs and vertebrae occurs via endochondral ossification in the cartilaginous growth plate, which is located at both ends of the growth plate (Karsenty G, Wagner E F 2002 Reaching a genetic and molecular understanding of skeletal development. Dev Cell 2:389-406; Olsen B R, et al. 2000 Bone development. Annu Rev Cell Dev Biol 16:191-220). One autocrine regulator of bone growth is C-natriuretic peptide (CNP) (Hagiwara H, et al. 1994 Autocrine regulation of rat chondrocyte proliferation by natriuretic peptide C and its receptor, natriuretic peptide receptor-B. J Biol Chem 269:10729-10733; Hagiwara H, et al. 1996 cGMP produced in response to ANP and CNP regulates proliferation and differentiation of osteoblastic cells. Am J Physiol 270:C1311-C1318; Suda M, et al. 1996 C-type natriuretic peptide as an autocrine/paracrine regulator of osteoblasts. Biochem Biophys Res Commun 223:1-6; Yasoda A, et al. 1998 Natriuretic peptide regulation of endochondral ossification. Evidence for possible roles of the C-type natriuretic peptide/guanylyl cyclase-B pathway. J Biol Chem 273:11695-11700; Mericq V, et al. 2000 Regulation of fetal rat bone growth by C-type natriuretic peptide and cGMP. Pediatr Res 47:189-193), a member of the natriuretic peptide hormone family which circulates at a very low level, suggesting that it has very little systemic activity on bone (Kalra P R, et al. 2001 The role of C-natriuretic peptide in cardiovascular medicine. Eur Heart J 22:997-1007; Daggubati S et al. 1997 Adrenomedullin, endothelin, neuropeptide Y, atrial, brain, and C-natriuretic prohormone peptides compared as early heart failure indicators. Cardiovasc Res 36:246-255).
Studies using primary cultures of osteoblast-like cells and chondrocytes have revealed that natriuretic peptides with short half-lives such as CNP and atrial natriuretic peptide (ANP) can regulate proliferation and differentiation of osteoblasts and chondrocytes (Hagiwara H, et al. 1994 Autocrine regulation of rat chondrocyte proliferation by natriuretic peptide C and its receptor, natriuretic peptide receptor-B. J Biol Chem 269:10729-10733; Hagiwara H, et al. 1996 cGMP produced in response to ANP and CNP regulates proliferation and differentiation of osteoblastic cells. Am J Physiol 270:C1311-C1318; Suda M, et al. 1996 C-type natriuretic peptide as an autocrine/paracrine regulator of osteoblasts. Biochem Biophys Res Commun 223:1-6; Yasoda A, et al. 1998 Natriuretic peptide regulation of endochondral ossification. Evidence for possible roles of the C-type natriuretic peptide/guanylyl cyclase-B pathway. J Biol Chem 273:11695-11700; Mericq V, et al. 2000 Regulation of fetal rat bone growth by C-type natriuretic peptide and cGMP. Pediatr Res 47:189-193). CNP stimulates the intracellular messenger cyclic GMP (cGMP) 10-fold more in chondrocytes than ANP (Hagiwara H, et al. 1994 Autocrine regulation of rat chondrocyte proliferation by natriuretic peptide C and its receptor, natriuretic peptide receptor-B. J Biol Chem 269:10729-10733). cGMP itself is important for bone development and plays a role in regulating growth and differentiation of osteoblasts (Hagiwara H, et al. 1996 cGMP produced in response to ANP and CNP regulates proliferation and differentiation of osteoblastic cells. Am J Physiol 270:C1311-C1318; Suda M, et al. 1996 C-type natriuretic peptide as an autocrine/paracrine regulator of osteoblasts. Biochem Biophys Res Commun 223:1-6; Yasoda A, et al. 1998 Natriuretic peptide regulation of endochondral ossification. Evidence for possible roles of the C-type natriuretic peptide/guanylyl cyclase-B pathway. J Biol Chem 273:11695-11700; Mericq V, et al. 2000 Regulation of fetal rat bone growth by C-type natriuretic peptide and cGMP. Pediatr Res 47:189-193, Pfeifer A, et al. 1996 Intestinal secretory defects and dwarfism in mice lacking cGMP-dependent protein kinase II. Science 274:2082-2086; Yasoda A, et al. 2004 Overexpression of CNP in chondrocytes rescues achondroplasia through a MAPK-dependent pathway. Nat Med 10:80-86).
Genetic deletion of CNP or its signaling results in severe skeletal dysplasias caused by reduced chondrocyte proliferation and differentiation (Chusho H, et al. 2001 Dwarfism and early death in mice lacking C-type natriuretic peptide. Proc Natl Acad Sci USA 98:4016-4021; Yoder A R, et al. 2008 Reduced ability to C-type natriuretic peptide (CNP) to activate natriuretic peptide receptor B (NPR-B) causes dwarfism in 1bab −/− mice. Peptides 29:1575-1581). In mice lacking CNP, dwarfism and early death occur (Chusho H, et al. 2001 Dwarfism and early death in mice lacking C-type natriuretic peptide. Proc Natl Acad Sci USA 98:4016-4021). At birth, these mice have a 10% reduction in bone length, but the growth retardation becomes more severe postnatally and 70% of the mice die in the first 100 days after birth (Chusho H, et al. 2001 Dwarfism and early death in mice lacking C-type natriuretic peptide. Proc Natl Acad Sci USA 98:4016-4021). Cartilage-specific overexpression of CNP partially rescues the achondroplasia dwarfism of the CNP-deficient mice, suggesting that CNP stimulates bone growth through direct effects on chondrocytes (Yasoda A, et al. 2004 Overexpression of CNP in chondrocytes rescues achondroplasia through a MAPK-dependent pathway. Nat Med 10:80-86). Contrarily, mice with overexpression of CNP in cartilage have prominent skeletal overgrowth (Yasoda A, et al. 2004 Overexpression of CNP in chondrocytes rescues achondroplasia through a MAPK-dependent pathway. Nat Med 10:80-86). Overexpression of CNP has also been associated with overgrowth and bone abnormalities in a 14-year-old girl (Bocciardi R, et al. 2007 Overexpression of the C-type natriuretic peptide (CNP) is associated with overgrowth and bone anomalies in an individual with balanced t(2;7) translocation. Hum Mutat 28:724-731). Functional inactivation of the natriuretic peptide (NPR)-B receptor that binds CNP (Tamura N, et al. 2004 Critical roles of the guanylyl cyclase B receptor in endochondral ossification and development of female reproductive organs. Proc Natl Acad Sci USA 101:17300-17305; Tsuji T, Kunieda T 2005 A loss-of-function mutation in natriuretic peptide receptor 2 (Npr2) gene is responsible for disproportionate dwarfism in cn/cn mouse. J Biol Chem 280:14288-14292) or gene encoding for cGMP protein kinase II through which cGMP effects are mediated also produces dwarfism (Pfeifer A, et al. 1996 Intestinal secretory defects and dwarfism in mice lacking cGMP-dependent protein kinase II. Science 274:2082-2086; Miyazawa T, et al. 2002 Cyclic GMP-dependent protein kinase II plays a critical role in C-type natriuretic peptide-mediated endochondral ossification. Endocrinology 143:3604-3610; Teixeira C C, et al. 2008 Nitric oxide, C-type natriuretic peptide and cGMP as regulators of endochondral ossification. Dev Biol 319:171-178).
CNP and ANP are ring-structured natriuretic peptides with very short half-lives of <3 min in the circulation (Kalra P R, et al. 2001 The role of C-natriuretic peptide in cardiovascular medicine. Eur Heart J 22:997-1007, Teixeira C C, et al. 2008 Nitric oxide, C-type natriuretic peptide and cGMP as regulators of endochondral ossification. Dev Biol 319:171-178; Nakao K, et al. 1986 The pharmacokinetics of α-human natriuretic polypeptide in healthy subjects. Eur J Clin Pharmacol 31:101-103; Yandle T G, et al. 1986 Metabolic clearance rate and plasma half life of alpha-human atrial natriuretic peptide in man. Life Sci 38:1827-1833). Their biologic effects last for <30 min. Vessel dilator is a linear natriuretic peptide synthesized by the ANP gene (Brenner B M, et al. 1990 Diverse biological action of atrial natriuretic peptide. Physiol Rev 70:665-699; Vesely D L 2003 Natriuretic peptides and acute renal failure. Am J Physiol Renal Physiol 285:F167-F177; Vesely D L 2007 Natruiretic hormones. In: Alpern R J, Herbert S C (eds.) Seldin and Giebisch's The Kidney: Physiology and Pathophysiology. 4th ed. Elsevier, Inc., Amsterdam, The Netherlands, pp 947-977) that has a circulatory half-life of 107 min (Ackerman B H, et al. 1997 Disposition of vessel dilator and long-acting natriuretic peptide in healthy humans after a one-hour infusion. J Pharmacol Exp Ther 282:603-608) and its biologic effects last >6 h (Vesely D L, et al. 1994 Three peptides from the atrial natriuretic factor prohormone amino terminus lower blood pressure and produce diuresis, natriuresis, and/or kaliuresis in humans. Circulation 90:1129-1140).
The compositions currently used for treatment of skeletal disorders have a short-lived in vivo residence. It would therefore be beneficial to develop longer-lived compounds, facilitating fewer treatments with improved effect.